Although methane is abundant, its relative inertness has limited its utility in conversion processes for producing higher-value hydrocarbons. For example, oxidative coupling methods generally involve highly exothermic and potentially hazardous methane combustion reactions frequently require expensive oxygen generation facilities and produce large quantities of environmentally sensitive carbon oxides. Non-oxidative methane conversion is equilibrium-limited, and temperatures ≧ about 800° C. are needed for methane conversions greater than a few percent.
Catalytic processes have been proposed to co-convert methane and ethylene to higher hydrocarbons. For example, a process disclosed in Heterocyclic Dissociation of C—H Bond of Methane over Ag+-exchanged Zeolites and Conversion of Methane into Higher Hydrocarbons in the Presence of Ethene or Benzene, T. Baba and K. Inazu, Chemistry Letters, 35 (2), 142-147, 2006, involves the heterocyclic dissociation of methane over silver cationic clusters in Ag+-exchanged zeolites in the presence of an ethylene co-feed. The dissociation leads to the formation of silver hydride and methyl cations, which react with the ethylene co-feed to produce propylene.
Since ethylene is itself a valuable hydrocarbon, processes are desired which produce higher molecular weight unsaturated hydrocarbons from methane without the need for unsaturated co-reactants, such as ethylene. It would also be beneficial if such processes did not produce large amounts of low-value saturated hydrocarbon (e.g., ethane) and could be operated such that the relative amounts of C2 unsaturates and C3 unsaturates in the product are adjustable.